Strabismus is a misalignment of the eyes. It can be either acquired or congenital. There are many different types of strabismus. Strabismus is classified by the direction of the misaligned eye. Common types of strabismus include esotropia, where one eye is turning inward toward the nose,exotropia, where one eye is turning outward towards the ear and hypertropia, where one eye is higher than the other.

Causes of strabismus

There are many different causes of strabismus. The majority of these are related to a problem with the neuromuscular communication between the brain and the extraocular muscles. Three of the twelve cranial nerves (III, IV, VI) are responsible for eye movement. These can be weak or nonfunctional (palsy) and cause strabismus.

Intraocular and extraocular causes

Strabismus can also be caused by something occluding the child's visual axis such as a congenital cataract, a droopy eyelid, or a lesion on the eyelid or inside the orbit pushing against the eye. It can be caused by an asymmetric refraction, also known as the glasses’ prescription (ex: one eye is more farsighted than the other), or a large difference in astigmatism between the two eyes.

Common associations with strabismus:

Some common associations seen with strabismus are prematurity, Down Syndrome, congenital craniofacial anomalies and genetic disorders.

What is amblyopia?

Amblyopia is decreased vision in one or both eyes due to abnormal development of the visual pathway in infancy or childhood. In the first few years of life, the brain must learn to see or interpret the images seen by both eyes as one cohesive image. In amblyopia, the brain receives a poor image from the eye that is either misaligned or not seeing well due to other causes mentioned above. In turn, the brain focuses its attention to the better seeing eye. This leads to the visual nerve pathways between the brain and the misaligned eye not achieving proper stimulation and the visual centers of the brain do not develop normally. In amblyopia, there may not be an obvious problem of the actual eye itself.  It is, however, a leading cause of vision loss in children.

How does trauma cause strabismus?

Trauma can cause strabismus by inducing brain damage that impairs control of eye movement. It can damage the nerves that control eye movement and there can be damage of the eye muscles either directly or secondarily from trauma to the eye socket. Below is an example of an orbital floor fracture with an entrapped eye muscle (see arrow). This is an emergency, and the eye can look completely normal.

How is strabismus treated?

The goal of strabismus treatment is to optimize the vision in both eyes, improve eye alignment, and hopefully improve the ability of both eyes to work together. Treatment options can include eyeglasses, patching of the good eye, eye exercises, prism, and eye muscle surgery.

References:

1) https://aapos.org/glossary/strabismus

2) https://webeye.ophth.uiowa.edu/eyeforum

3) https://emj.bmj.com/content/30/10/836

Written by Caroline Watson, M.D.

Instagram @high_myope

Biography:

Dr. Watson was born and raised in Louisiana. She attended college at Florida State University, received a bachelor's in both biology and exercise physiology. She graduated from UAB medical school and is currently a PGY4 Ophthalmology Resident. In July, she will begin an advanced refractive cataract surgery and anterior segment fellowship in Clearwater, FL. She lives in Louisiana with her husband, an aerospace engineer, and their three children.